[tempus2016]

Builds on the previous PR in this batch (fix/editor-colour-picker-targets).

fix(cards): give the Family Goal and Photo Gallery cards a visual editor

Opening either card in the dashboard editor showed "Visual editor not
supported", so they could only be set up in YAML. Both now open a visual
editor like the other TaskMate cards. The Family Goal card takes the
overview entity, an optional title (blank shows the goal's name), the
card design and the header colour. The Photo Gallery card takes the
activity entity, an optional title, how many photos to show (blank shows
them all), the card design and the header colour. Every label and helper
is translated, the card's defaults stay out of the YAML, and the YAML
editor round-trips. The editors load only when opened.

fix(cards): keep the Family Goal card's header when no goal is set

With no family goal switched on, the Family Goal card showed only its
"No family goal set" placeholder, so a title, header colour or design
picked in its editor made no visible difference in the preview. The
card now draws its header in every state: the title (or "Family goal"),
in the header colour and card design, with the placeholder beneath.
The Photo Gallery card already kept its header with no photos; it and
the Family Goal card now also keep it when the entity can't be found.

Testing

• Unit and frontend tests for this change are included in the diff; the whole batch passes the full suite.
• Checked on the dev Home Assistant instance as part of the v7.7.1 pre-release gate (desktop and 360/375/393/768 phone/tablet widths).